A braking system for a vehicle includes a flat disc or rotor that is fixed to and rotatable with an associated vehicle wheel and a caliper that is fixed to the vehicle chassis spans the rotor. A pair of friction surfaces or pads retained by the caliper are urged by pressurized fluid acting on a piston and the caliper housing into engagement with opposed rotor faces to effect a brake application. When the pressurized fluid is released the resiliency of a seal associated with the piston moves the piston and caliper housing to provides sufficient running clearance between the pads and the rotor. In some instances, a controlled rotor wobble or run-out is desirable to supplement the restorative force of the resilient seals to retract pads from the rotor after a braking event. However excessive wobble or other deviations from opposed flat surfaces orthogonal to the wheel axis can cause brake chatter, excessive rotor wear and other undesirable results. Thus, it is desirable to maintain dimensional tolerances between the rotor and brake pads. It is also desirable to easily inspect brake rotors to determine if the dimensional tolerances are being met as well as for signs of abnormal wear and manufacturing or material defects. These inspections may be performed during manufacture or subsequently after the rotor has been installed on a vehicle.
Brake rotors have been inspected on a vehicle through a dial indicator magnetically fastened to a suspension component. The dial indicator reading is recorded while rotating the wheel, but the method provides only run-out data for one brake plate surface. When further investigation is needed, the rotor is removed from the vehicle and sent to the manufacturer's or supplier's warranty center where a precision spindle and a controller are used to rotate the rotor at a constant speed. Even under controlled laboratory conditions, speed variations may sometimes undermine the accuracy of the test results.
U.S. Pat. No. 5,970,427 discloses a disc brake testing device having a pair of gauges on opposite disc sides and aligned with one another to measure thickness and lateral run-out of a brake disc that may be employed when the disc is surrounded by a wheel and dust shield. Several varieties of contact as well as non-contact gauges or probes are disclosed. The device may be employed in a computer operated testing system and may compare test results with industry standards. The position measurements are taken by the pair of gauges as a function of the disc position, and are frequently taken in a periodic manner which is either time-dependent or dependant on the angular position of the disc relative to the pair of gauges. Time-dependent measurements may be provided by employing a clock circuit which reads the position measurement output of the gauges at a certain point in a timing cycle. Angular position-dependent measurements may be taken by providing an incremental reference index of the relative position of the gauges with respect to the disc, and reading the position measurement output of the gauges as each increment is passed. If the position signals are analog in character, then an A/D converter is provided for converting the position signals into digital signals which may be processed by a microprocessor which serves as means for processing the position signals to determine the thickness and lateral run-out of the disc. The A/D converter may also amplify or otherwise condition the position signals as necessary to provide digital signals which are compatible with the microprocessor. In addition to communicating with the A/D converter to receive the digital signals, the brake testing system has an instruction set which contains instructions for directing the microprocessor to operate on the digital signals to generate characterizing data which indicate the condition of the disc. The instruction set can be either code which can be accessed by the microprocessor, or may be imbedded in the microprocessor. The characterizing data typically include the lateral run-out of the brake disc as well as a characterization of the thickness of the disc, such as the average of all instantaneous thickness measurements taken. Typically, for lateral run-out, the standard values have only a maximum allowable value for lateral run-out. If the calculated value for the lateral run-out is less than or equal to the maximum allowable value, the disc is considered to fall within acceptable limits for lateral run-out. For average thickness, the standard values typically include a minimum allowable thickness value, and may additionally include a “machine to” value. Thickness variation may also be calculated as part of the thickness characterization. If the thickness variation is less than or equal to a maximum variation standard value, the thickness variation of the disc is considered to be acceptable. However, U.S. Pat. No. 5,970,427 makes no mention of rotor speed compensation, harmonic analysis, or interpolation, all of which are desirable features and provide for rotor analysis of far greater scope and accuracy.
Thus, the prior art is capable of providing rather limited information about a rotor being tested. However, the information is limited to average high and low region values and the number of such regions sensed.
It would be highly desirable to provide each specific high and low value as well as the angular location of each such high or low value.
It would also be highly desirable to provide sufficient accurate data from a rotor to perform a wide variety of rotor analyses and diagnostics.